Most people are inundated with advertisements and contest announcements. Some of those promotions -- like this one from Starbucks or this one from Ben & Jerry's -- promise the chance to win a year's supply of a product in exchange for a person's contact information. How do companies determine how much is in a year's supply?

Using common sense. There is no legal definition of "a year's supply," which means that companies may choose an amount they think will last a year. Legally, an offer of a year's supply must be accompanied by a disclaimer defining exactly what that supply entails: how much it is, its retail value, when and how it will be delivered to the winner, and whether the winner must meet any requirements to receive the prize. Offers of a year's supply must also pass a "reasonableness test" to comply with advertising laws. This means that a reasonable person would agree that the amount defined in the disclaimer would last an average individual for a year. Most large companies that hold sweepstakes have lawyers on hand to make sure that their claims pass legal muster.

Usually, companies define a year's supply based on the assumption of regular daily or weekly consumption of a product. For instance, a year's supply of Ben & Jerry's is defined as 52 pints, one for each week of the year. For the Starbucks K-Cup giveaway, a year's supply is defined as 52 10-count packages of K-Cups. The winners of a Zone Bar promotion receive 365 ZonePerfect bars in their three favorite flavors. Hy-Vee, a Midwestern grocery chain, gave away 365 Tide Pods this year. (A pod suffices for one load of laundry.) You might eat more than a pint of ice cream a week or do less than one load of laundry per day, but it's easy to see how all of these examples pass the reasonableness test. Less intuitive are some cumulative rather than incremental amounts: For instance, ClickInks.com estimates a year's supply of printer ink to be worth $100.

Sometimes when people win a year's supply of something, they receive not the product itself -- shipping 52 pints of Cherry Garcia would be a logistical challenge -- but coupons redeemable in stores for the product. Other times, as with the ZonePerfect bars, the manufacturer sends the product itself to the winner. Whether the winner receives vouchers or the product itself should be made explicit in the official contest or sweepstakes rules.

What about when companies offer a lifetime's supply of something? As with a year's supply, the amount is finite and must be explained in the official sweepstakes or contest rules. Sometimes, as with this gumball giveaway, the sweepstakes creators use average human lifespan and average rate of consumption to calculate a typical lifetime supply (in this case, 22,083 gumballs). Other times, as with the Center for Biological Diversity's condom giveaway from 2010, the lifetime supply is a round number presented without explanation. The Center for Biological Diversity pinned a lifetime supply at 1,000 condoms, which, assuming a 60-year adult lifespan, breaks down to about 17 condoms a year.